The studies proposed in this application are a logical continuation of our past and ongoing investigations which seek to achieve a more complete understanding of the mechanisms of tooth enamel formation and the means by which fluoride influences those mechanisms. They are of clinical relevance in the quest to enhance the caries preventive effects of systemic fluorides while minimizing the risk of fluorosis. The studies also take advantage of unique characteristics of enamel formation to obtain new knowledge concerning the basic processes common to formation of all mammalian hard tissues and the effects of fluoride on such processes. The proposed project includes five specific aims: (1) to measure the fluoride content of enamel and its relative capacity for fluoride uptake during its various stages of development by using 3H-mannitol to correct for water loss that occurs during enamel collection and the assay procedure; (2) to determine by physical assay methods the relative amount of fluoride associated with the mineral and the organic phases of secretory stage developing enamel; (3) to determine if the enamel organ contains fluoride at significantly higher levels than plasma or other soft tissues; (4) to use in vitro methods to explore directly the possibility that sodium is the counter-ion for movement of fluoride from the extracellular fluid through the enamel; and (5) to measure the caries preventive effect of the same total fluoride dose (0.1 mu gm/gm b.w.) given during the first half of enamel formation, during the last half of enamel formation, or at half the daily dose throughout enamel formation. On the basis of our previous studies we have developed a general hypothesis for the uptake and retention of fluoride in developing enamel. The specific aims listed above are designed to explore important questions concerning that hypothesis and test its validity.